1. Field of the Invention
The present invention relates to a protective film for various members. More particularly, it relates to a paint composition, a process for producing a transparent protective film using the same, and organic glass provided with a transparent protective film.
2. Description of the Related Art
Silicone-based films have been used widely as protective films for various members, because they are good in terms of the heat resistance, wear or abrasion resistance and insulative property. The silicone-based films are usually siloxane-based cured paint films, and are formed by dehydrative condensation of alkoxysilanes using the sol-gel process. However, the silicone-based films produced by the sol-gel process have lattice defects in the silica network-shaped structure, and exhibit physical properties different from those of quartz glass. Moreover, when giving the silicone-based films physical properties equivalent to those of quartz glass, it is required to remove the lattice defects from the silicone-based films by sintering them at a high temperature of 200° C. or more. Accordingly, the silicone-based films produced by the sol-gel process are not desirable for applications to members made of resins whose heat resistance is poor. Consequently, it has been carried out recently to use precursor polymers, such as polysilazane, which undergo the conversion reaction into silica even at room temperature in order to produce synthetic silica whose physical properties are equivalent to those of quartz glass.
Note that the superficial wear or abrasion resistance of members to sliding operations depends on the surface hardness of members. However, high-hardness films using polysilazane independently are likely to crack or come off from the substrate. Hence, Japanese Unexamined Patent Publication (KOKAI) No. 9-175,868 discloses to mix polysilazane with an organic polymer, such as acrylic resins, in order to improve the wear or abrasion resistance of the resulting hard coat films by increasing the film thickness thereof.
However, when polysilazane is simply mixed with acrylic resins as disclosed in Japanese Unexamined Patent Publication. (KOKAI) No. 9-175,868, phase separation occurs so that the resulting mixtures are inhomogeneous mixtures in which the components are not mixed with each other. When such inhomogeneous mixtures are turned into hard coat films, the resultant hard coat films become clouded. Moreover, no hard coat films can be produced which exhibit a sufficient degree of transparency, because they are so thickened that the particles of polysilazane have scattered light. Thus, it is difficult to produce a protective film, which exhibits high transparency and a high surface hardness simultaneously, using the process disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 9-175,868.